Taximeter

ABSTRACT

A taximeter in which taxi speed is represented by an analogue signal, the analogue signal controlling the frequency of a variable frequency oscillator and an indicated taxi fare read out being obtained by counting pulses from the oscillator to display a fare charge the rate of advancement of which is thus dependent upon the magnitude of the analogue signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

This invention relates to taximeters.

2. Description of Prior Art:

Mechanical taximeters generally employ two rotatable elements, one ofwhich is driven by a motor at a constant rotational speed, and the otherof which is driven usually indirectly, from the taxi wheels or gear boxor speedometer cable at a rate which is proportional to the speed of thevehicle. Clutch means is provided operating to couple an output shaft towhichever of the two rotatable elements is rotating at the greaterspeed. This shaft drives a metering and display mechanism to display afare charge corresponding to the number of rotations of the outputshaft. The indicated fare will thus advance at a constant rate when thevehicle is stationary as the output shaft will be driven at a constantspeed or "time" rate by the rotatable element which is coupled to amotor. On the other hand, when the vehicle is travelling at a speedgreater than a predetermined speed, the fare is advanced at a rateproportional to the distance or "mileage" being travelled by thevehicle, the output shaft in this case being driven by that rotatableelement which is coupled to the taxi wheels, gear box or speedometercable.

Mechanical taximeters are somewhat disadvantageous in that they employnumerous parts which are prone to wear and require constant servicing.This difficulty has been sought to be overcome by providing electronicdigital taximeters which replace the mechanical clutch, the rotatableelements and the motor for driving one of the elements by a fixedfrequency oscillator, to represent the time rate, and a variablefrequency generator, generating a signal the frequency of which isvaried in proportion to the speed of the vehicle. These oscillatorsproduce pulse streams, and suitable electronic selector means isprovided to select whichever of the two pulse streams is at the highestfrequency and apply this to advance a fare couter. Whilst thesearrangements require virtually no moving parts, and are inherently quitereliable, they are still disadvantageous in that it is possible to losea pulse from each pulse stream during transitions caused by switching ofthe selected pulse stream from the mileage pulse stream to the timepulse stream. Such lost pulses result in loss of revenue and the losscan be significant in cases where frequent mileage time transitionsoccur, such as in city driving. An object of the invention is to atleast substantially avoid this difficulty.

BRIEF DESCRIPTION OF THE INVENTION

According to the invention there is provided a taximeter comprisinggenerator means for generating a generator analogue signal representingthe speed of a taxi with which the meter is to be used, and fareread-out means coupled to said generator means for displaying a farecharge which is advanced in dependence upon said analogue signal at arate which, when the taxi meter is coupled to a taxi, is proportional tothe speed of the taxi.

The fare read-out means may be arranged such that the displayed farecharge is not advanced in dependence upon said analogue signal when thecondition of the analogue signal is such as to correspond to movement ofa taxi to which the taxi meter is fitted at less than a predeterminedspeed. Alternatively, the fare read-out means may be arranged such thatthe displayed fare charge is not advanced in dependence upon saidgenerator analogue signal when the generator analogue signal has notbeen in a condition indicative of motion of a taxi to which the meter isfitted for more than a predetermined time period.

In the first case, the fare read-out means preferably includes areference source for generating a reference analogue signalrepresentative of said predetermined speed of said vehicle and selectormeans coupled to receive and compare the analogue signals generated bysaid generator means and by said source to control the rate of fareadvanced in dependence upon the reference analogue signal when thegenerator analogue signal is indicative of a lesser speed than saidpredetermined speed and in dependence upon the generator analogue signalwhen the speed represented thereby is greater than said predeterminedspeed. Preferably, too, in this case, the fare read-out means furthercomprises a taxi meter wherein said fare read-out means includes anoscillator coupled to receive the selected one of said analogue signalsfrom said selector means and operates to generate an output signalhaving a frequency which is fixed when said reference analogue signal ispassed thereto and which is at a frequency proportional to the speedindicated by the generator analogue signal when this is passed thereto,counter and display means also being provided in said fare read-outmeans and coupled to receive said output signal and operating to countindividual pulses thereof and to display visually said fare inaccordance with pulses so counted. In the second case, the fare read-outmeans preferably includes an oscillator coupled to receive saidgenerator analogue signal via time delay circuit means which delays saidgenerator analogue signal by said predetermined time period, saidoscillator generating an output having a frequency which is fixed, whensaid analogue signal is indicative of zero taxi speed, and which is at afrequency proportional to taxi speed when the generator analogue signalis indicative of taxi speed above zero, counter and display means alsobeing provided in said fare read-out means and coupled to receive saidoutput signal and operating to count individual pulses thereof anddisplaying visually said fare in accordance with pulses so counted.

In either instance, the generator analogue signal is preferably a DCvoltage directly proportional to the taxi speed, and the oscillator is avoltage controlled oscillator.

The invention also provides a taxi meter including a variable frequencyoscillator, counter and display means for counting output pulses fromthe oscillator and displaying a fare charge in proportion to pulsescounted, generator means for generating an analogue signal representingthe speed of a taxi to which the meter can be fitted and control meanscontrolling the frequency of said oscillator in accordance with saidanalogue signal, at least when said signal is above a predeterminedlevel or has been above a predetermined level for a predetermined time.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE ACCOMPANYING DRAWING

The invention is further described with reference to the accompanyingdrawings in which:

FIG. 1 is a block schematic diagram of one form of taxi meterconstructed in accordance with the invention;

FIG. 2 is a diagram of the electrical circuit of a DC tacho generatorincorporated into the taxi meter of FIG. 1;

FIG. 3 is a diagram of the electrical circuit of a DC voltage selectorincorporated into the taxi meter of FIG. 1;

FIG. 4 is a diagram of the electrical circuit of a voltage controlledoscillator incorporated into the taxi meter of FIG. 1; and

FIG. 5 shows a modification to the taxi meter of FIG. 1.

DETAILED DESCRIPTION

The taxi meter 10 shown in FIG. 1 includes a direct current tachogenerator 12 having an input shaft coupled to, for example, thespeedometer cable of the taxi or to the gear box or to the wheelsthereof so that the shaft is driven at a rate proportional to thevehicle speed. The tacho generator provides a direct current outputproportional to the speed of the vehicle. A fixed direct current voltagesource 14 is also provided, the output of this representing time. Theoutputs from the tachometer 12 and source 14 are fed to a direct currentvoltage selector 16 which selects whichever of the two voltagesgenerated by tacho generator 12 and source 14 is highest and passes thisto a voltage controlled oscillator 14. The voltage controlled oscillatorhas a variable frequency output, the frequency being proportional to theoutput voltage from selector 16. Output pulses produced by theoscillator are fed to a counter 21 which operates to advance a farereadout display means 22 to display a fare which is advanced at a rateproportional to the pulse rate on line 20.

When the taxi to which the taxi meter 10 is attached is stationary, thetacho generator 12 produces zero output and voltage selector 16 thusprovides, at its output, the voltage provided by source 14. Thus, whenthe taxi is stationary, the output frequency of oscillator 18 isconstant and the fare displayed by the display means is advanced at aconstant "time" rate. When the taxi accelerates from rest, the voltageprovided by tacho generator 12 increases until, at a predeterminedvehicle speed, it exceeds the voltage provided by source 14. In thiscase, then, the counter advances the displayed fare at a rateproportional to the speed of travel of the taxi.

Tacho generator 12 is shown in FIG. 2. It includes a disc 40 secured toan axle 42, which axle comprises the input shaft of the generator. Disc40 has a plurality of radial slots 44 extending inwardly from itsperiphery and a light source 46 positioned to one side of the disc sothat light can pass to the other side only when a slot 44 is positionedin the path of light from the source 46. Light source 46 comprises alight emitting diode which is coupled to electrical source 14 via apositive supply rail 52 and a ground line 50. A photocell 48 ispositioned to the side of disc 40 remote from source 46 so that itreceives light only each time a slot 44 is positioned in the path oflight from source 46. Electric current pulses produced by the photocell48 pursuant to successive illuminations thereof as disc 40 rotates, arepassed to an amplifier 54 and thence to a monostable multi-vibrator 56.Amplifier 54 and multi-vibrator 56 are powered from line 50 and rail 52.

Multi-vibrator 56 is triggered off the trailing edges amplified pulsesfrom photocell 48 and produces a pulse train on an output line 58therefrom. Pulses of this pulse train are of constant amplitude and areof the same freguency as pulses fed to the multi-vibrator but haveconstant pulse width. These pulses are passed to a three stage RC filter60 which comprises three series connected resistors 62 and threecapacitors 64 each coupled to rail 52 and respectively to the successiveresistors 62 at sides of the resistors remote from multi-vibrator 56.Output from filter 60, as measured between rail 52 and line 66 fromfilter 60, comprises a smoothed analogue signal voltage, the amplitudeof which is directly proportional to the frequency of signal applied online 58 and thus also directly proportional to the speed of rotation ofdisc 40.

DC voltage selector 16 (FIG. 3) comprises an operational amplifier 68one input of which is coupled to line 66 to receive signal fromgenerator 12. The output side of the amplifier is coupled to one side ofa diode 70, the other side of the diode being connected via a line 72 ina feed-back loop to the other input of amplifier 68. Line 72 is coupledto an output line 90, to positive supply rail 52 via a variable resistor74 and to ground line 50 via a resistor 76. The operation of DC selector62 is such that in the event that the voltage between rail 52 and line66 is less than that which line 72 would assume if this voltage were tobe determined only as the proportion of the supply voltage between rail52 and line 50 as established by the division ratio of resistors 74 and76, then line 90 will assume the latter voltage. On the other hand, ifvoltage between rail 52 and line 66 exceeds such voltage, then lines 72and 90 will assume the voltage of line 66. Thus, the operation is suchthat when the taxi is stationary, and disc 40 is also consequentlystationary, line 90 will assume the fixed proportion of the supplydetermined by the ratio of resistors 74 and 76 and will remain at thisvoltage, as the taxi accelerates from rest, until a stage is reached atwhich the voltage between rail 52 and line 66 is greater, whereuponvoltage of line 90 will be proportional to speed of the taxi. It is inthis way that the transition from computing of fares at a time rate tocomputing them at a distance travelled rate is accomplished.

It is possible to so adjust resistor 74 that immediately any substantialvoltage is present on line 66 pursuant to the taxi beginning to movefrom rest, the voltage on line 90 will follow that on line 76. This modeof operation is sometimes desirable to give a distance only farecomputation with no time rate fare charge.

Referring now to FIG. 4, the voltage-controlled oscillator 18 comprisesa precision current source 100 which operates to provide a current on anoutput line 110 therefrom which is directly proportional to the voltageon line 90 from voltage selector 16. Source 100 includes an operationalamplifier 112, one input of which is coupled to line 90 and a transistor114. Transistor 114 has its emitter connected to supply rail 52 via aresistor 116 and its collector connected to line 110. The base isconnected via a line 120 to the output from amplifier 112 and theemitter of the transistor is coupled in a feed-back line 124 to thesecond input of amplifier 112. The interconnection of the amplifier 112and transistor 114 is such that current flow from line 52 throughtransistor 114 to line 110 is regulateed so as to be proportional to themagnitude of the voltage difference between rail 52 and line 90.

Line 110 is coupled to an astable multi-vibrator 102 which forms asecond part of voltage controlled oscillator 18. This includes atransistor 132 having its emitter connected to ground line 50, its baseconnected to positive supply rail 52 via a resistor 134 and having itscollector connected to a resistor 136. A second transistor 130 has itsemitter coupled to rail 52 and its collector connected to a resistor138. Resistors 138 and 136 are connected, at ends remote from thecollectors of the respective transistors 130 and 132, at a junction 133.Junction 133 is connected to one side of a capacitor 140. The other sideof the capacitor is connected both to line 110 from current source 100and to the base of a third transistor 142. Transistor 142 has itsemitter connected to ground line 50 and its collector connected to oneside of a resistor 144, the other side of resistor 144 being coupled torail 52 via a resistor 146. A diode 150 is connected from the collectorof transistor 142 to one side of a capacitor 154, the other side ofcapacitor 154 being connected to the base of transistor 132. Thejunction 135 between diode 150 and capacitor 154 is coupled to groundline 50 via resistor 160 and to rail 52 via a resistor 162. The base oftransistor 130 is coupled to the junction 137 between resistors 144 and146.

The operation of multi-vibrator 102 will be described as beginning froma state in which transistors 130 and 142 are both off and transistor 132is on. It is assumed, firstly, that capacitor 140 has just been chargedto a voltage approaching the voltage between line 50 and rail 52, withthe side thereof coupled to junction 133 being substantially at groundpotential, owing to transistor 132 being on, and with the other sidethereof being below ground potential. In this condition, capacitor 140will receive current from line 110 and will charge at a rateproportional to current flow therefrom. After a time which will beproportional to the rate of current flow on line 110, capacitor 140 willbe charged such that the voltage at the side thereof connected to thebase of transistor 142 will be sufficient to turn transistor 142 on,since the collector of this transistor is coupled directly to thepositive supply via resistors 144 and 146 and the emitter is coupled toground at line 50. Prior to this turning on of transistor 142,transistor 130 is held in the off condition by virtue of there being novoltage applied to the base thereof, however, when transistor 142 isturned on, the end of resistor 144 which is coupled to the collector oftransistor 142 assumes substantially ground potential and resistors 144and 146 thus act as a voltage divider across line 50 and rail 52 so thatjunction 137 and the base of transistor 130 assume a voltage which turnstransistor 130 on.

Resistor 160 is substantially greater than resistor 162 and the side ofcapacitor 154 which is coupled to the junction 135 of these thereforeassumes, prior to turning on of transistor 142 when no current flowthrough the diode 150 occurs, a substantial positive voltage which isarranged to be somewhat greater than the potential of the other side ofcapacitor 154 which is coupled to the base of transistor 132. Capacitor152 thus assumes a charged state. When transistor 142 is turned on, thejunction between diode 150 and capacitor 154 is immediately placed atsubstantially ground potential because current flow from rail 52,through resistor 162 the diode and transistor 142 to ground can occurand the charge voltage of the capacitor is applied to the base oftransistor 132 thus causing the base to assume a voltage which is wellbelow ground potential thereby turning off transistor 132. The charge oncapacitor 154 is dissipated relatively quickly, the capacitor thencharging in the reverse polarity from supply rail 52. As this chargingoccurs, the voltage of the base of transistor 132 rises until it issufficient to again turn on transistor 132. The time interval for whichtransistor 132 is on is arranged to be a very small period, of the orderof 1 millisecond.

In the period when transistor 132 is turned off, capacitor 140 cancharge from rail 52 via transistor 130 and resistor 138. It will thusassume a charge voltage approaching the supply voltage, the side of thecapacitor being coupled to junction 135 reaching approximately thesupply voltage and the side coupled to the base of transistor 142 beingsubstantially at ground potential. The time constant of the chargingcircuit for the capacitor is arranged such that the capacitor can reacha steady fully charged voltage within the short period in whichtransistor 132 is off.

When transistor 132 is turned on pursuant to charging of capacitor 154,the side of capacitor 140 which is connected to the collector oftransistor 132 via resistor 136 is effectively placed at a voltage closeto earth potential so that the charge voltage of capacitor 140 iseffectively applied across the emitter base junction of transistor 142to cause the base to assume a negative voltage relative to the emitterthereby to turn off transistor 142. As soon as transistor 142 is turnedoff, transistor 130 is likewise turned off and the circuit is readiedfor another cycle.

Output from multi-vibrator 102 is taken from the collector of transistor132. This output comprises a series of output pulses, produced at eachinterval when transistor 132 is off. These pulses are of short durationand are separated by periods directly proportional to the appliedvoltage between line 90 and rail 52. By this means it is assured thatthe oscillator possesses linear input voltage frequency characteristics.

The counter 21 and display 22 may be of a type known well in the artemploying, for example, decade counters which drive conventional numeraldisplay devices. The rate of fare advancement may be varied byappropriate selection, in the counter, of the number of pulses whichneed to be received from oscillator 18 before advancement of theindicated fare is effected by one unit.

In the taxi meter 25 of FIG. 5, the output from tachometer 12 is fed,instead of to selector 16, to a voltage delay device 24 which operatesto delay the output from the tacho generator. This delayed output, online 26, is passed to an oscillator 30 of the kind having an outputfrequency which is fixed when there is no voltage on line 26, but whichis proportional to the output voltage on line 26 when such voltage ispresent. Output from the voltage controlled oscillator is passed tocounter 21 and display 22. The arrangement of FIG. 5 operates in ananalogous way to the embodiment of FIG. 1, except that as output fromtacho generator 12 rises upon acceleration of the taxi from rest, therise in voltage is delayed so that the switching of the oscillator tothe condition where its output is dependent upon the tacho generatoroutput is delayed to correspond to occurrence of a predetermined taxispeed.

Voltage delay 24 may comprise a simple RC circuit such as that providedby the filter 60 of FIG. 2. The RC circuit should have a relatively longtime constant sufficient to delay rise in voltage on line 26 by a shorttime interval. Oscillator 30 may be of the same form as oscillator 18except for modification of current source 100 in a manner known per seto provide a constant current flow on line 110 when there is no signalon line 90 thereto and to provide a proportionally rising output currenton line 110 when voltage on line 90 increases. Alternatively, it could,of course, merely comprise the oscillator 18 together with the source 14and voltage selector 16 described.

In both described embodiments, the tacho generator 12 may be electronicor electromechanical but in any event preferably has an output which isa direct current voltage proportional to angular velocity of an inputshaft thereof.

Because the oscillators 18 or 30 operate continuously, there is no lossof pulses when switching between the two operative conditions thereof iseffected. Whilst the described arrangement utilises a direct currentanalogue voltage to represent the speed of the taxi this speed could berepresented, for example, by a direct current.

The described construction has been advanced merely by way ofexplanation and many modification may be made thereto without departingfrom the spirit and scope of the invention as defined in the appendedclaims.

The claims defining the invention are as follows:
 1. A taximetercomprising:generator means for generating a generator analog signalrepresenting the speed of a taxi with which the meter is to be used; areference source for generating a reference analog signal representativeof a predetermined speed of said vehicle; selector means coupled toreceive and compare the analog signals generated by said generator meansand by said source; and fare read-out means coupled to said selectormeans for displaying a fare charged which is advanced in dependence uponthe reference analog signal when the generator analog signal isindicative of a lesser speed than said predetermined speed and independence upon the generator analog signal when the speed representedthereby is greater than said predetermined speed.
 2. A taximeter isclaimed in claim 1 including an oscillator coupled to receive theselected one of said analog signals from said selector means andoperable to generate an output signal having a frequency which is fixedwhen said reference analog signal is passed thereto and which is at afrequency proportional to the speed indicated by the generator analogsignal when the generator analog signal is passed thereto; andwhereinthe fare read-out means includes counter and display means coupled toreceive said output signal and operating to count individual pulsesthereof and to display visually said fare charge in accordance withpulses so counted.
 3. A taximeter is claimed in claim 2 wherein:saidgenerator means generates said generator analog signal as aunidirectional electrical signal the magnitude of which is directlyproportional to the speed of the vehicle; said reference analog signalis generated by said source as a uni-directional electrical signal ofconstant magnitude; said selector means is operative to pass whicheverof these electrical signals is the greater to said oscillator; and saidoscillator is of the kind in which the frequency of generation of outputsignals therefrom is directly dependent upon the magnitude of theelectrical signal applied thereto.
 4. A taximeter as claimed in claim 3wherein:said analog signals are generated in the form of DC voltages;and said oscillator is a voltage controlled oscillator.